1. Field of the Invention
The present invention relates to a process and apparatus for the combustion of hydrocarbon gases, and more particularly but not by way of limitation, to an improved process and apparatus for substantially smokeless combustion of hydrocarbon gases and mixtures thereof with other constituents.
2. Discussion
In the handling of hydrocarbon liquids, such as gasoline, kerosene, diesel fuel and the like, air-hydrocarbon gas mixtures are readily produced which cannot be vented directly to the atmosphere due to the resulting pollution of the environment and fire hazard. Common loading facilities involving trucks and marine tankers, storage tanks and numerous other industrial operations all have potential for such pollution and fire hazard. Consequently, a variety of processes and apparatus have been developed and used for removing hydrocarbon vapors from air-hydrocarbon vapor mixtures so that the remaining air can be safely vented to the atmosphere.
Recovery type of prior art processes include adsorption vapor recovery systems for recovering hydrocarbon vapors from air-hydrocarbon mixtures expelled as a result of storage breathing of vented hydrocarbon vessels. One such process is disclosed in U.S. Pat. No. 4,066,423, issued to McGill and Scott, wherein the hydrocarbon vapor components are adsorbed from the mixture so that substantially hydrocarbon free air can be safely vented to the atmosphere. Other recovery prior art processes have utilized refrigeration systems to condense the emitted gases.
Another type of prior art system for the disposal of hydrocarbon vapors utilizes a flare system for burning the hydrocarbon vapors. Because of the variances in the pressure of the vapors being passed through the flare systems, problems are often encountered in maintaining a substantially constant pressure drop through the flare system to ensure stable operation. It is known that flaring of low pressure hydrocarbon gases having a molecular weight ratio of hydrogen to carbon of less than about 0.30 tends to produce smoke because of incomplete combustion and the formation of free carbon. To overcome this smoke problem several methods and apparatus have been employed in prior practice, such as the introduction of a smoke suppressant (i.e. steam or water into the combustion zone); the use of air-powered flares to provide turbulent mixing of air with the hydrocarbon gas for complete smokeless combustion; and the flaring of both high and low pressure gases in a single flare structure by utilizing the energy of the high pressure gas to provide the required turbulent air and gas mixture for complete combustion.
U.S. Pat. No. 4,105,394, issued to Reed, Zink and Schwartz, discloses a single flare structure which utilizes the energy of the high pressure gas to provide the required turbulent air and gas mixture for complete combustion of hydrocarbon vapors. In the Reed, et al. patent the high and low pressure burner apparatus are incorporated into a single flaring structure which is served by a single relief line so that the process does not require simultaneous venting of low and high pressure gases. A pressure control unit is attached to the relief line to sense pressure and permit gas flow to the high pressure burner apparatus above predetermined pressures.
While many of the prior art vapor recovery and disposal devices, including those taught by the above-mentioned patents, have achieved varying degrees of success, such devices have variously been expensive to fabricate and to operate; have experienced high maintenance costs; or have not provided for a substantially constant pressure drop through flare devices when such devices encounter wide ranging vapor flow rates.